Neurotrophic factors have been shown to appear in the rat brain after lesion. This project intends the molecular cloning of the gene encoding for these lesion-induced trophic factors in the brain. First, we developed the assays to produce these factors and test for their neurotrophic activity. A fraction of mRNA, prepared from lesioned rat brain, responsible for neurotrophic activity was found by in vivo translation into proteins in Xenopus Laevis oocytes. This fraction is now being used to construct a cDNA library in the vector pGEM blue. We also constructed a cDNA library specific for lesioned rat brain in the vector bluescribe M 13. By differential colony hybridization, we have selected positive clones and some of these have been tested for coding for neurotrophic activity.